Positioning possibilities within wireless communication networks play an important role in modern communication systems and will probably be even more exploited in future development. Many different kinds of information available in different nodes can be utilized for positioning purposes. In order to be able to perform position determinations, positioning information has to be communicated between different nodes in a communication system. The reporting procedures and formats for positioning information therefore also play an important role in the communication systems. In that respect, one also has to consider the compatibility with e.g. different standards for reporting.
A basic positioning method in most cellular communication systems is based on identification of a cell ID. A certain cell is associated with a certain area and if a mobile terminal is connected to the cell it can be assumed that the mobile terminal is situated within the associated area, or at least close to the associated area.
This concept has fairly recently been further developed into a method referred to as Adaptive Enhanced Cell-ID (AECID) fingerprinting. By associating high-precision position measurements with tags typically comprising different kinds of connection information as well as auxiliary quantized measurements, clusters of measurements having the same or similar tags will be gathered in certain limited areas. Such information can then be used in analogy with the cell-ID positioning to obtain a position estimation from such type of information that is comprised in the tags, without need of any high-precision positioning techniques. In other words, fingerprinting positioning uses detailed geographical maps of radio properties of the cellular system, to position the terminal. This fingerprinting technology is already today provided as a part of a serving mobile location center (SMLC) node functionality for Global System for Mobile communications (GSM). The fingerprinting functionality is also being migrated to LTE, where the positioning node typically is denoted the enhanced SMLC (eSMLC). This AECID fingerprinting is e.g. described in the published international patent application WO 2008/118052 A1 or in the article “Adaptive Enhanced Cell-ID Fingerprinting Localization by Clustering of Precise Position Measurements” by T. Wigren in IEEE Transactions on Vehicular Technology, Vol. 56, No. 5, September 2007, pp. 3199-3209. A further use of Round Trip Time (RTT) measurements is described in “RTT Positioning in WCDMA” by T. Wigren and J. Wennervirta in Proceedings of the 5th International Conference on Wireless and Mobile Communications, ICWMC 2009, Cannes/La Bocca, France, pp. 303-308, Aug. 23-29, 2009.
The result of the clustering of measurements in AECID is an area definition. The most convenient representation of such an area is a polygon, due to the fact that the shape of the area may vary very much. The polygon is adapted to enclose a predetermined fraction of the clustered measurement results within an as small area as possible. Such areas are also easily reported over e.g. Wideband Code Division Multiple Access (WCDMA) and Long-Term Evolution (LTE) networks by standard formats.
In most areas covered by cellular communication systems, the lateral position is the most important parameter. However, in e.g. urban areas or mountain areas, also the altitude parameter may be of importance. The AECID approach can be augmented to also handle the altitude parameter. To that end, one approach has been used based on that a plane polygon is adapted to the lateral parameters and a height for each polygon corner has been established based on the clustered position measurements in the vicinity of each polygon corner. The result is a polygon in three dimensions.
One problem with such a representation of positioning data is that there are today no standardized formats for reporting of three-dimensional polygons. In the published International patent application WO2008/054271, a two-dimensional polygon reporting format was utilized in a non-standardized manner to report three-dimensional polygon data. This approach operates well in most cases but is, as mentioned, not standard compatible. In the published International patent application WO2010/069614, the three-dimensional polygon was approximated by a point with an uncertainty ellipsoid. That approach operates very well in many situations, e.g. for most smaller cells.
However, the approaches disclosed in prior art are not perfect in all respects, and in particular since the LTE development and further future developments will change the availability of as well as the request for accurate positioning, there is a general need for improving the positioning report alternatives.